Catheter ablation is a procedure to treat arrhythmias such as atrial fibrillation, a disease of the heart muscle characterized by abnormal conduction. Depending on the severity of the problem, multiple ablation procedures may be necessary to achieve effective results. This is because current electrophysiology (EP) technology has limitations in precisely locating the tissue to ablate that is the source of the abnormality.
The conventional diagnostic process starts with an electrocardiogram (ECG) taken from electrodes attached to the surface of the skin of a subject (e.g., a patient). A medical team evaluates the ECG signal and determines whether medication and/or ablation are/is indicated. If ablation is indicated, an EP study is performed. A catheter is inserted into the heart via the patient's neck or groin and the electrical activity of the heart is recorded. Based on this EP study, ablation is performed on the area(s) of the heart that the medical team suspects is causing the abnormal heart rhythm(s).
An ablation catheter is inserted into the patient's blood vessel and guided to the site of the tissue that is causing the abnormal electrical propagation in the heart. The catheter may use different energy sources (the most common being heat or cold) to scar the tissue, reducing its ability to initiate and/or transmit abnormal electrical impulses, which eliminates the abnormal heart rhythm. ECG signals are recorded from a surface electrode on a patient's skin, and intracardiac (IC) signals may be obtained from catheters inside the patient's heart and recorded as an electrogram (EGM). Both ECG and IC (EGM) signals are small signals that require conditioning and amplification to be accurately evaluated.
In conventional EP systems, to confirm whether the ablation treatment of a certain tissue site is successful, the medical team must often stop the ablation process and collect physiologic signals (e.g., cardiac) from a monitoring device (e.g., ECG monitor). This is because current systems do not allow accurate simultaneous detection, acquisition, and isolation of small cardiac signals (amplitude in the range of 0.1-5 mV and frequency in the range of DC to 1 KHz) in near real-time during the application of large ablation signals (on the order of a few hundred volts at frequencies around 450 kHz).
Specifically, U.S. Patent Application Publication No. US 2006/0142753A1 to Francischelli, et al. propose a system and method for ablation and assessing their completeness or transmurality by monitoring the depolarization ECG signals from electrodes adjacent to the tissue to be ablated. Francischelli, et al. point out that, to minimize noise-sensing problems during measurements of the ECG signals from the electrodes on the ablation device, the measurements are preferably made during interruptions in the delivery of ablation energy to the ablation electrodes.
Generally, some current EP recording systems can effectively support treatment of arrhythmias such as atrial flutter and supra ventricular tachycardia, which show up as large-amplitude, low-frequency signals. However, more complex and prevalent arrhythmias, such as atrial fibrillation and ventricular tachycardia, which are characterized by low-amplitude, high-frequency signals, have not found effective evaluation of all relevant signals.
This signal detection, acquisition, and feature extraction can be further complicated by equipment line noise and pacing signals. To reduce noise and artifacts from the various electrical signal information, current EP recorders use low-pass, high-pass, and notch filters. Unfortunately, conventional filtering techniques can alter signals and make it difficult or impossible to see low-amplitude, high-frequency signals that can be inherent in cardiac monitoring, the visualization of which signals could help treat atrial fibrillation and ventricular tachycardia. It has been recently recognized that the assurance of waveform integrity, such as for low noise acquisition of IC and ECG signals in an EP environment, had not been previously accomplished due to contamination by artifacts and noise.
Specifically, in an article titled Waveform Integrity in Atrial Fibrillation: The Forgotten Issue of Cardiac Electrophysiology (Annals of Biomedical Engineering, Apr. 18, 2017), Martinez-Iniesta, et al. point out that high-frequency and broadband equipment noise is “unavoidably recorded” during signal acquisition, and that further complications of acquisition result from a variety of other signals, including 50 or 60 Hz electrical mains, high-frequency patient muscle activity, and low-frequency baseline wander from respiratory or catheter movements or unstable catheter contact. Martinez-Iniesta, et al. further point out that regular filtering causes significant alteration of waveforms and spectral properties, as well as poor noise reduction. Yet aggressive filtering between 30 and 300 Hz is still a routine EP practice.
Conventional practices distort morphological features in resulting signals, causing loss of relevant (of interest) signal information and affecting signal validity. Martinez-Iniesta, et al. propose a partial software solution for only mid- and high-frequency noise reduction using preprocessing and de-noising methods, yet no solution exists combining low-frequency noise-reduction components in software with noise-reduction components in hardware. A desired feature of EP systems is the ability to preserve the integrity of original signal information using a combination of hardware and software that can reduce noise from signals (or promote a high signal-to-noise ratio) while minimizing hardware filtering that would otherwise remove signal content of interest.
Currently, the predominant approach for ablation treatment of paroxysmal and persistent atrial fibrillation is pulmonary vein isolation (PVI), wherein a medical team, using a cardiac mapping system, recreates the heart geometry in 3D and performs ablation on anatomical locations such as the pulmonary vein from which the atrial fibrillation emanates. The procedure is a long 2-8 hours, and a physician may not achieve a durable lesion/scar to isolate the tissue causing the problem from the left atrium. Thus, patients are often required to return for additional ablation procedures to complete the treatment. However, additional ablation procedures, and possible complications, can be minimized by being able to clearly visualize the cardiac signals during ablation and determine whether an ablation lesion is transmural.
Conventional EP systems may suffer from several other limitations. First, a user often wants to process and display multiple features of signals in near real-time. For example, a medical team may want to simultaneously display various and multiple versions of ECG, IC, and other physiologic signals in near real-time to evaluate different signal attributes. But conventional EP systems are often unable to simultaneously process and display multiple versions of signals in near real-time.
Second, a user often wants to dynamically apply a new digital signal processing function to a signal without interfering with other digital signal processing functions already being applied to the signal. But conventional solutions do not enable a user to dynamically apply a new digital signal processing function to a signal without stopping the capture of the signal, or interfering with other digital signal processing functions already being applied to the signal.
Finally, a user often wants to synchronize the processing and display of multiple signals in near real-time. For example, a user may want to synchronize the display of multiple processed versions of the same signal. Further, a medical team may want to synchronize the display of multiple processed versions of ECG, IC, and other physiologic signals. This is because the ability of the medical team to make an effective clinical diagnosis may depend on comparing multiple signals at the same point in time. But conventional solutions may not be able to process and synchronize the display of multiple processed signals in near real-time.